1. Field of the Invention
The present invention relates to an image forming system that can control electrical power supplied to peripheral devices connected to an image forming apparatus.
2. Description of the Related Art
Copying machines, printers, or facsimile machines are in many cases used with the electrical power supply being left on all the time. A reduction in the electrical power consumption of such apparatuses is desirable.
An electrophotographic image forming apparatus includes a fixing unit that fuses a toner image onto paper by heat. A fixing unit consumes much of the electrical power supplied to the image forming apparatus. Thus, it is important to reduce electrical power consumed by the fixing unit in order to reduce the total electrical power consumption. Currently, a type of power-saving of the image forming apparatus is widely used, which has a power-saving mode in which the temperature of the fixing unit is decreased. Recent image forming apparatuses have a power-saving mode in which, when a second image forming operation has not been started for a predetermined period of time after completing first image forming operation, the temperature of the fixing units is decreased.
Thus, in the power-saving mode, electrical power consumption is reduced by stopping or reducing the supply of electrical power to the fixing unit. When the power-saving mode is released, initialization is performed in the image forming apparatus. When initialization is performed in the image forming apparatus, a fusing temperature, at which a toner image can be sufficiently fused, needs to be quickly reached by supplying sufficient electrical power to the fixing unit. However, there is a limit on electrical power that can be supplied at one time. For example, in Japan, when electrical power is supplied from an ordinary socket, the maximum electrical power is 1500 W for one circuit. Thus, when electrical power of 1500 W or more is needed for startup, a special electrical power line, for example, a specific socket, is needed, thereby significantly impairing the versatility and installability of the apparatus.
In view of this problem, an image forming apparatus is proposed in Japanese Patent Laid-Open No. 2002-014574, which includes a plurality of energy supply units that can supply electrical power within the image forming apparatus. In such an image forming apparatus, the time of transition from a power-saving status (power-saving mode) to a standby status (standby mode) in which said image forming apparatus is ready to start an image forming operation can be reduced regardless of the power rating of a socket.
In general, various types of optional device (herein, also called an accessory or a peripheral device) that expand the functions of an image forming apparatus can be connected to the image forming apparatus at the user's request. A typical optional device is a high-capacity paper deck, a stapler unit, a paper folding unit, a sorting unit, a punching unit, an inserting unit, a cutting unit, an automatic document feeder, or a glossing unit. A high-capacity paper deck can feed a large number of sheets of paper. A stapler unit staples sheets of paper on which images are formed. A paper folding unit folds sheets of paper. A sorting unit sorts sheets of paper. A punching unit punches holes in sheets of paper. An automatic reversing document feeder is used when images are formed on both sides of a sheet of paper. An inserting unit inserts sheets of paper of one type between sheets of paper of another type. A cutting unit can cut a large number of sheets of paper all at once. An automatic document feeder automatically feeds a document into a reading position. A glossing unit gives a gloss to an image formed on a sheet of paper. In general, such optional devices operate using electrical power supplied from an image forming apparatus to which the optional devices are connected.
However, there is a problem with the foregoing known image forming apparatus. Namely, the image forming apparatus needs to include a high-capacity energy supply unit that can supply electrical power to a plurality of energy supply units. This increases the size and cost of the image forming apparatus.
Furthermore, during initialization of the image forming apparatus, initialization of optional devices connected to the image forming apparatus is executed in parallel. In initialization of optional devices, for example, operations of the individual optional devices and any remaining sheet of paper are checked. Thus, the image forming apparatus can supply to the fixing unit only as much electrical power as the maximum electrical power of 1500 W minus electrical power necessary for initialization of the optional devices.
Since the optional devices are connected to the image forming apparatus on the user's request at any time, it is presumed that all of the optional devices are connected to the image forming apparatus regardless of whether the optional devices are actually connected to the image forming apparatus. Thus, only as much electrical power as the maximum electrical power minus electrical power necessary for the optional devices can be supplied to the fixing unit.
Although the maximum electrical power is entirely available to the image forming apparatus when the image forming apparatus is used with no optional device being connected to the image forming apparatus, sufficient electrical power cannot be used by the image forming apparatus when such optional devices are connected. That is to say, since only as much electrical power as the maximum electrical power minus electrical power necessary to operate all of the optional devices is available, the startup of the image forming apparatus is delayed, and electrical power consumption and unnecessary cost are increased.